Abdennacer Ahmanache - Academia.edu (original) (raw)
Papers by Abdennacer Ahmanache
Journal of Laser Applications, 2017
Laser cutting of thick metal workpieces requires the use of low operating speeds which, however, ... more Laser cutting of thick metal workpieces requires the use of low operating speeds which, however, will have an influence on the cut quality following the used laser wavelength. In this study, we develop a model which takes into account the Fresnel coefficients in order to determine the local laser absorbed energy as a function of the beam incidence angle on the surface workpiece. The deposited laser energy occurs on the metal/air interface which evolution is tracked by the volumeof-fluid multiphase model. In the simulation, in order to find the difference between the patterns obtained on the kerf walls when different laser wavelengths are used, an important number of cells must be used at the regions of interest, which are characterized by high gradients, but a larger number of cells will have the consequence to complete the calculation with much less computer time consumption. Therefore, a gradient adaption method was implemented in order to control the number of cells, by multiplying or reducing them when it is necessary, depending on the importance of the temperature gradients. It was found out in our results that processing with higher wavelength (k CO2 ¼ 10.6 lm) results in lower roughness on the kerf walls, compared to the surface quality obtained by using lower wavelength (k Nd-YAG ¼ 1.06 lm). A good accordance with the experimental observations is concluded. V
200 p. : ill. ; 30 cmNous présentons une étude numérique du transfert de chaleur et de l’écouleme... more 200 p. : ill. ; 30 cmNous présentons une étude numérique du transfert de chaleur et de l’écoulement d’un fluide métallique en convection naturelle dans une cavité cylindrique avec parois chaudes et un échangeur thermique à la base1 Cette cavité représente le creuset d’un four de croissance cristalline1 L’étude est menée en fonction du facteur de forme de la cavité, de la dimension de l’échangeur thermique, et des propriétés thermo-physiques du fluide exprimées à travers le nombre de Prandtl et le nombre de Rayleigh. Les résultats sont présentés sous la forme des isothermes, des lignes de courant, du nombre de Nusselt local et moyen et de la température moyenne de la cavité pour des nombres de Rayleigh allant de 103 à 108. Deux matériaux extrêmes sont étudiés : le Silicium, matériau semiconducteur à très bas nombre de Prandtl (Pr=0.013) et le Germanate de Bismuth (Bi4Ge3O12) : un oxyde à haut nombre de Prandtl (Pr=20). On montre que le nombre de Rayleigh, le nombre de prandtl et la d...
Thermal Science, 2013
Numerical study of natural convection heat transfer and fluid flow in cylindrical cavity with hot... more Numerical study of natural convection heat transfer and fluid flow in cylindrical cavity with hot walls and cold sink is conducted. Calculations are performed in terms of the cavity aspect ratio, the heat exchanger length, and the thermo physical properties expressed via the Prandtl and the Rayleigh numbers. Results are presented in the form of isotherms, streamlines, average Nusselt number, and average bulk temperature for a range of Rayleigh number up to 10 6. It is observed that Rayleigh number and heat exchanger length influences fluid flow and heat transfer, whereas the cavity aspect ratio has no significant effects.
Journal of Laser Applications, 2017
Laser cutting of thick metal workpieces requires the use of low operating speeds which, however, ... more Laser cutting of thick metal workpieces requires the use of low operating speeds which, however, will have an influence on the cut quality following the used laser wavelength. In this study, we develop a model which takes into account the Fresnel coefficients in order to determine the local laser absorbed energy as a function of the beam incidence angle on the surface workpiece. The deposited laser energy occurs on the metal/air interface which evolution is tracked by the volumeof-fluid multiphase model. In the simulation, in order to find the difference between the patterns obtained on the kerf walls when different laser wavelengths are used, an important number of cells must be used at the regions of interest, which are characterized by high gradients, but a larger number of cells will have the consequence to complete the calculation with much less computer time consumption. Therefore, a gradient adaption method was implemented in order to control the number of cells, by multiplying or reducing them when it is necessary, depending on the importance of the temperature gradients. It was found out in our results that processing with higher wavelength (k CO2 ¼ 10.6 lm) results in lower roughness on the kerf walls, compared to the surface quality obtained by using lower wavelength (k Nd-YAG ¼ 1.06 lm). A good accordance with the experimental observations is concluded. V
200 p. : ill. ; 30 cmNous présentons une étude numérique du transfert de chaleur et de l’écouleme... more 200 p. : ill. ; 30 cmNous présentons une étude numérique du transfert de chaleur et de l’écoulement d’un fluide métallique en convection naturelle dans une cavité cylindrique avec parois chaudes et un échangeur thermique à la base1 Cette cavité représente le creuset d’un four de croissance cristalline1 L’étude est menée en fonction du facteur de forme de la cavité, de la dimension de l’échangeur thermique, et des propriétés thermo-physiques du fluide exprimées à travers le nombre de Prandtl et le nombre de Rayleigh. Les résultats sont présentés sous la forme des isothermes, des lignes de courant, du nombre de Nusselt local et moyen et de la température moyenne de la cavité pour des nombres de Rayleigh allant de 103 à 108. Deux matériaux extrêmes sont étudiés : le Silicium, matériau semiconducteur à très bas nombre de Prandtl (Pr=0.013) et le Germanate de Bismuth (Bi4Ge3O12) : un oxyde à haut nombre de Prandtl (Pr=20). On montre que le nombre de Rayleigh, le nombre de prandtl et la d...
Thermal Science, 2013
Numerical study of natural convection heat transfer and fluid flow in cylindrical cavity with hot... more Numerical study of natural convection heat transfer and fluid flow in cylindrical cavity with hot walls and cold sink is conducted. Calculations are performed in terms of the cavity aspect ratio, the heat exchanger length, and the thermo physical properties expressed via the Prandtl and the Rayleigh numbers. Results are presented in the form of isotherms, streamlines, average Nusselt number, and average bulk temperature for a range of Rayleigh number up to 10 6. It is observed that Rayleigh number and heat exchanger length influences fluid flow and heat transfer, whereas the cavity aspect ratio has no significant effects.